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Code: Selecteer alles

\documentclass[a4paper, 12 pt]{article}

..//..

\usepackage{tikz}

\usetikzlibrary{decorations.markings}

\usetikzlibrary{patterns}

..//..

\begin{document}

\begin{center}

\begin{tikzpicture}

\begin{scope}[thick,decoration={markings, mark=at position 0.5 with {\arrow{<}}}]

\draw[postaction={decorate}] (-2,0)--(2,0) node[below] at (0,0) {a};

\draw[postaction={decorate}] (2,0)--(2,3) node[right] at (2, 1.5) {b};

\draw[postaction={decorate}] (2,3)--(-2,3) node[above] at (0,3) {a};

\draw[postaction={decorate}] (-2,3)--(-2,0) node[left] at (-2,1.5) {b};

\draw[fill = red] (0,1.5) circle (1cm);

\draw[fill] (0,1.5) circle (0.03cm);

\end{scope}

\end{tikzpicture}

\end{center}

\end{document}

Code: Selecteer alles

size(6cm,0);

pair A=(-2,0), B=(2,0), C=(2,3), D=(-2,3);

filldraw(A--B--C--D--cycle,lightblue);

draw(Label("$a$",Relative(.5),S),B--A,linewidth(1.3),MidArrow(8));

draw(Label("$a$",Relative(.5),N),D--C,linewidth(1.3),MidArrow(8));

draw(Label("$b$",Relative(.5),E),C--B,linewidth(1.3),MidArrow(8));

draw(Label("$b$",Relative(.5),W),A--D,linewidth(1.3),MidArrow(8));

filldraw(circle((0,1.5),1),1bp+lightred);

dot((0,1.5));